Electrical linear actuators typically take the form of linear stepping motors and rotary stepping and brushless motors mechanically connected to lead-screw, ball-screw, planetary roller-screw and ‘Rohlix’ transmissions.
U.S. Pat. No. 4,234,831 ‘Compound rotary and/or linear motor’ relates to a compound rotary and/or linear motor. It has two interposed magnet systems of which at least one is variable by an electronic control system to generate rotary and/or linear motion of the other. One of the two magnet systems consists of axially consecutive arrangements, preferably rings, of electrically separate magnet poles. The other magnet system contains at least one pair of magnet poles. The electronic control system is designed optionally or according to program to generate rotary motion by sequentially energizing consecutive magnets in a ring, to generate linear motion by sequentially energizing axially consecutive magnets and to generate a combined linear and/or rotary motion by sequentially energizing consecutive magnets forming a helix.
Low torque actuators for heart valves that use helical arrays of alternating magnets are known from WO97/41633 A1 (EP0903003) ‘Rotary torque-to-axial force energy conversion apparatus’ that describes a highly specialised ventricle assist device for a heart. describes a rotary to linear actuator primary designed for use as a Total Artificial Heart (TAH) prosthesis.
JP61173659 A discusses an alternately polarised permanent magnetic helix. Alternating axial magnetic pole stripes extend the length of the rotor and match with machined stator grooves/notches. This approach theorises that the grooves in the rotor and gaps between the stator laminates could be used to increase flux reluctance and guide the rotor in a helical path. The “reluctance” approach is neither forceful nor efficient as an energy transduction and transmission method.
US2004/041474 describes a rotor that is moved helically due to the electromagnetic influence of a stator. Within this design the rotor and stator interdigitate. The permanent magnets attached to the rotor shaft are face magnetised parallel to the long axis of the rotor shaft.
JP10257751 describes a rotor with a multistart alternating magnetic thread propelled by a electromagnetic multipole stator with helical stator teeth. It describes a twin start magnet nut and bolt used as a means of converting rotary to linear movement.
There is a need for a linear actuator that has certain advantageous characteristics. For certain applications, an actuator should be compact, lightweight, powerful and efficient. Ideally it should also be highly integrated and provide a highly controllable transformation of electrical to mechanical energy. This technical agenda is driven by the attempt to make a practical and competitively performing actuator that can be portable, and may be used in prosthetics, robotics and automation.